Method of burning waste liquors



Nov. 3, 1959 F. w. HocHMu'rH 2,911,234

' METHOD oF BURNING WASTE LIQUoRs Filed June l, 1955 4 Sheets-Sheet 1 INI/ENTOR. 'y ,f

Frank W. Hochmuth 30 3f am A4 .ZW

34 ATTOMJE;

Nov. 3, 1959 F. w. HocHMuTH METHODvOF BURNING WASTE LIQUORS 4 Sheets-Sheet 2 Filed June l, 1955 I L.. L

INI/ENTOR.

Frank W. Hochmuth f1 TTOR NE Y Fig. 2.

Nov. 3, 1959 Filed June 1. 1955 Ummm F. W. HOCHMUTH METHOD oF BURNING WASTE LIQuoRs -4 Sheets-Sheet 5 /2 JNI/ENTOR.

Frank W. Hochmufh BY W TTORNEY F. w. HOCHMUTH 2,911,284

METHOD oF BURNING WASTE LIQuoRs Nqv. 3, 19259 4 Sheets-Sheet 4 Filed June l, 1955 mmf INI/ENTOR.

Frank W. Hochmuth /ITTORNE Y UnitedStates Patent O 2,911,284v lVIETHOD OF BURNING WASTE LIQUORS Frank W. Hochmuth, Scotch Plains, NJ., assignor to Combustion Engineering, Inc., New York, N. a corporation of Delaware Application June 1, 1955, Serial No. 512,383

5 Claims. (Cl. 23-48) This invention relates to the burning of waste liquors and particularly to an improved method for burning and recovering the chemicals from the residual liquors Vleft after wood or other cellulose material has been digested with certain chemical solutions and the cellulosic libres separated therefrom, with this digestion being one of the process steps in the manufacture of paper from such cellulose bearing material.

In the past it has been the practice to burn this liquor in vertically disposed furnaces by spraying the liquor into the furnace at a location well above the furnace bottom and introducing the primary air for supporting combustion of this liquor into the furnace at a location adjacent thebottom of the -furnace and the secondary air at a location intermediate the location of the introduction of the primary air and the location` of the introduction of the liquor. With this arrangement it was often necessary to decrease the amount of secondary air introduced into the @furnace below that desired for optimum efficiency of combustion since if the desired ar'nountof secondaryair to obtain'this optimum combustion efficiency were employed the velocity of the gases passing lupwardly through the liquor spray would be so great as to cause excessive carryover or entrainment of the liquor in these gasesv thereby decreasing the voperating efficiency of the furnace aswell as causing numerous difllculties in the boiler through whichfthese'gases are directed upon leaving the furnace.

' Infoperating these furnaces for the burning of and the recovery of the chemicals from these residual liquors the liquor which is sprayed into the furnace has a substantial moisture content with most of this moisture being driven from the liquor spray upon its introduction into the furnace because of the high temperature in the furnace and'the hot gases passing upwardly through the furnace and spray and with the remaining solid particles falling on torthe furnace hearth and forming a roughly truncated pile.' vDuring the `descent to the hearth some of the lighter volatiles are driven from these solid particles with the remaining voltages being liberated and the combustible material in the solids being burned in this pile that forms upon the hearth with this combustion being supported by theintroduction of preheated primary air which is directed generally over and upon this pile of material. With the volatile matter and the combustibles contained in this solid material being burned there remains upon the hearth only theY non-combustibles which includes the chemicals that are to be recovered along with traces of various impurities with these being smelted upon the hearth and removed by a suitable spout. Since the solid material that descends to the hearth is very light and uiy, some of this material is entrained in the upwardly moving stream of combustion gases with the chemicals in this. material being softened or melted with a portion of these ,chemicals being deposited upon the walls of the furnace and thenk flowing down these walls to the bottom ofthe furnace. This causes the walls of the furnaceto be coated with a downwardly flowing layer of chemicals for a vconsiderable distance from the bottom of the furnace and which in practice extends well above the location at introduction of the liquor into the furnace was for the purpose of obtaining as much heat as possible in the zone intermediate introduction of this liquor and the bottom of the furnace since it was thought that this was necessary in order to obtain the required heat for evaporating a majority of the moisture from the liquor prior to its being 'deposited upon the hearth. However, with the present invention it has been established that it is unnecessary to introduce the secondary air below the introduction of the liquor into the furnace for this reason and that suillcient drying of the fuel will be had if only the primary air is introduced below this location.

In accordance with the present invention the residual liquor is sprayed into the furnace at a predetermined location above the furnace bottom and the primary air is introduced into the furnace at a location adjacent the bottom so that a majority of the liquor is dried and the combustible therein burned below this location of fuel introduction with the walls of the furnace being coated with a downwardly flowing layer of molten chemicals for a `distance well above this location of liquor introduction. Secondary air is introduced into the furnace at a location slightly above the location of liquor introduction and the material entrained in the upwardly rising stream of combustion gases which comprises dried solids and softenedV chemicals is subjected to this secondary air as this material rises through the furnace. The secondary air is introduced into the furnace so that it has a whirling motion imparted to it to create a whirling gas mass rotating about a generally vertical axis. Upon passing through this gas mass a portion of the dry solids as well as any volatiles therein are burned (the secondary air supporting this combustion) and the non-combustibles as well as any unburned solid combustibles have `a whirling or rotary motion imparted to them so that at least a portion of them are thrown by centrifugal force against the walls ofthe furnace and into the downwardly flowing layer of molten chemicals thereby separating this material lfrom the gas stream which passes outwardly from the furnace and over suitable heat exchange surface which generally takes the form of a boiler.

With this method of operation not only may the quantity of secondary air be regulated in accordance with the amount of air required for optimum combustion efciency without the danger of creating excessive carryover into the boiler but the secondary air is effective to separate solid material from the combustion gases with the greater the amount of secondary air the more effective it is as a separator.

It is an object of this invention to provide an iinproved method of operating a chemical recovery furnace.

Other and further objects of the invention will become apparent to those skilled in the art as the description proceeds wherein reference will be had to the accom panying drawing in which:

Figure 1 is a sectional elevational view of a chemical recovery unit constructed to operate in accordance with the improved method of this invention.

Figure 2 is a transverse sectional view through the furnace of this recovery unit taken generally along lines 2 2 of Fig. 1. e

Figure 3 is a fragmentary vertical section through the furnace at the location of the introduction of secondary air into the furnace and taken generally along line 3-3 into the furnace and showing in detail the manner'oi introduction of this air.

-Referring now to the drawing, wherein like reference characters are used throughout to designate like elements, the recovery unit depicted therein comprises the furnace which has its walls lined with exposed and closely spaced tubes "l2 that are connected into the boiler 14 which is associated with the furnace so as to receive from the furnance the combustion gases generated therein. Residual liquor that is obtained in the chemical digestion process of paper manufacture is introduced into furnace l@ at the or location 16 through nozzles i8 which are constmctcdand arranged in such a manner that the liquid spray does not touch the walls of the furnace or at 'most only a small portion of the spray touches these walls, the spray from a nozzle being a function of nozzle design as is well recognized. Because of the intense heat inthe 'furnace i@ and the upwardly rising stream of combustion gases passing through zone lo a. majority of the moisturein the liquor is immediately evaporated with the solid particles falling downward through the upwardly rising stream of combustion gases and forming a pile 2l? "with `this combustidn'stipporting air and 'with the noncombustibles as well as any unburned solid combustibles having a rotary or whirling motion imparted thereto by this whirling air mass so that a portion of them are thrown out by centrifugal force into the layer or coating of molten chemicals that is flowing downwardly along the furnace walls causing this material to be entrained in these molten chemicals and carried to the bottom of the furnaceand thereby effectively removing the'material from the combustion gases which otherwise wouldremainentr'ainedth'erein'and be' carried over into boiler 14.

The reduction in carryover of suspended material in the combustion gases from the furnace int'o the boiler over that heretofore obtained in chemical 'recovery units is effected first, because the secondary air is introduced above the point of liquor admission, thus reducing the gas velocity through the liquor spray zone and second, by

` the action of rotating the secondary air mass in throwing upon yhearth 22 with further moisture being driven from j these solids during their descent to the hearth.

Prior to being deposited upon hearth 22 the lighter volatiles may be driven from. the solids and burned, with the remainder of the volatiles being distilled upon the hearth and consumed along with the carbonaceous material in the solids.

The solids of this liquor are made up of combustibles which are volatiles and carbonaceous material and noncombustibles which are essentially the chemicals that are to be recovered along with-minor traccs'of impurities. These solids after being dried are very light and fluffy so that a certain portion of them, principally the smaller particles, are entrained in and move along with the upwardly rising stream of combustion gases with some of the combustibles being burned and with some of the non-combustibles being melted during their upward travel through the furnace with the combustion gases. This results in the Walls of furnace l0 being covered with a layer of molten chemicals which continuously descend downwardly along these walls to the bottom of the furnace with the upper limit of this layer or coating extending well above zone 16, as for example, the level indicated at 24.

However, notwithstanding this entrainment in the combustion gases, a major portion of the combustibles in the liquor sprayed into the furnace is burned upon the pile 20, and to support this combustion primary air is introduced through inlets 26 and directed generally upon this pile with this air being forced through these inlets from manifold 28 and duct 30 by fan 32 and with this air being preheated to a desired temperature by a suitable air preheater such as the steam preheater diagrammatically represented at 34.

The secondary air is introduced into furnace 10 at zone 36 which is spaced slightly above zone 16 but below level 24 and with this introduction of secondary air being in such a manner as to create a whirling air mass rotating generally about a vertical axis. For the accomplishment of this result, in the illustrative organization, the secondary air is introduced into the furnace through four sets of nozzles or inlet conduits 38 that are located generally adjacent the corners of the furnace and are disposed so the air streams issuing therefrom are tangent to an imaginary cylinder coaxial with the furnace with the nozzles in each set being preferably in a common planenormal to the furnace axis and with the sets of nozzles being vertically spaced as shown in Figs. l, 3, and 4. By introducing the secondary air in this manner a whirling mass of air is created which rotates generally about the vertical axis of furnace 10 and as the material entrained in the upwardly flowing stream of combustion gases enters this zone 36 it is engaged by the whirling air mass with a portion of thecombustibles in this material being burned upon coming into intimate contact suspended material outwardly into the layer of molten chemicals flowing down the furnace walls. Furthermore, with the secondary air introduced in accordance with this invention more complete combustion as well as more efcient combustion is had within the furnace than has heretofore been the case in these units since not only may as much secondary air as is `desired be introduced into the furnace -without fear of excessive carryover but fbecause the air is introduced tangentially, thereby creating a turbulent whirling air mass, there will be moreiintimate contact between the air and the suspended particles passing through the air mass. This increase in combustion efficiency in the furnace eliminates or substantially reduces secondary combustion at the entrance'of the boiler which has heretofore occurred and thus reduces the gas temperature entering the boiler.

A further effect of the improved operating method of this invention is to provide a more uniform temperature gradient across the boiler of the gas leaving the furnace and entering the boiler. This is important because the boiler is provided with rows of tubes uniformly spaced across the width of the boiler, such as superheater panels 42 in the illustrative organization, and it is advantageous to have these rows of tubes be subjected to' gases of substantially the same temperature in order to prevent overheating and other undesirable effects.

It will thus be seen that with vthe improved operating method of this invention an increase in the efficiency, usefulness and versatility in chemical recovery units yis achieved with limitations heretofore imposed upon'these units no longer being determining factors in their operation.

While the invention has herein been described with relation to a particular illustrative organization, it is to be understood that this is merely for the purpose of explaining the invention and is not to be considered as limiting the same since modifications within the scope of the invention may readily occur to those skilled in the art to which the invention pertains.

What I claim is:

1. In a vertically disposed chemical recovery furnace within which the combustibles in the residual liquor obtained in the chemical digestion process of cellulose bearing material in the manufacture of paper is burned, with the walls of the furnace being covered with downwardly owing molten 'chemical for a predetermined distance above the bottom of the furnace and with the chemicals in the liquor being collected is the bottom of the furnace and the combustion gases passing upwardly through'and out of the furnace, the improvement comprising the steps of spraying the liquor into the furnace at a given location intermediate the bottom of the furnace and the upper limit of the coating of molten chemical on the furnace walls with most of the liquor remaining free of contact of the furnace walls and descending toward the furnace bottom, introducing the primary air for supporting combustion into the furnace adjacent the bottom. thereof and bottom, drying a major portion of the liquor, burning the combustibles and smelting the chemicals in said vmajor portion in the furnace below said given location with minor amounts of solids being entrained in the upwardly moving gas stream, introducing additional air for supporting combustion into the furnace above said given location but below the upper limit of the coating of molten chemical on the furnace walls, said additional air being introduced through the furnace walls in streams that are spaced about the periphery of the furnaceand are di- Irected in such a manner as to create a whirling mass of gas generally at said location rotating about a generally vertical axis and disposed so the upwardlyY rising gases therebelow must pass therethrough` and thesolids entrained therein will intimately contact said mass of gas, subjecting the gases rising upwardly through the furnace together with the material entrained therein to this whirling gas mass, burning a portion of the combustibles in said material upon contact with this mass, imparting a whirling motion to the material upon being subjected to this whirling mass of gas and depositing through the centrifugal force thus developed a portion thereof into the molten chemicals owing down the furnace walls and removing smelted chemicals from the lower end of the furnace.

2. In a chemical recovery unit forrecovering the chemical in the residual liquor obtained in the chemical digestion process of cellulose bearing material in the manufacture of paper and utilizing a portion of the heat content of said liquor which unit includes a vertically disposed furnace having its outlet for combustion gases adjacent its upper end and a heat exchanger downstream of said outlet relative to combustion gas flow and that receives combustion gases from the furnace and abstracts a portion of the heat therefrom, with the liquor being sprayed into the furnace at a location spaced above the furnace bottom with most of the liquor remaining free of contact of the furnace walls and the primary air introduced at a location adjacent the furnace bottom and in a direction generally upon a pile of solids from the liquor collected on the furnace bottom with the liquor descending through the hot combustion gases rising upward through the furnace thereby drying the same so that a majority of the liquor burns at the bottom of the furnace with portions of unburned dried liquor solids as Well as non-combustibles being carried upward with the upward owing gas and with suflicient smelted chemicals being carired along therewith and contacting the walls of the furnace so the walls of the furnace for a distance well above the location of the introduction of the liquor into the furnace become coated with molten chemicals that descend therealong to the furnace bottom, the improvement comprising introducing additional combustion supporting air into the furnace at a location above the introduction of the liquor but below the upper limit of the coating of molten chemical on the furnace walls, said additional air being introduced in streams through the furnace walls with the streams being spaced about the periphery of the furnace and directed in a manner to create a whirling gas mass generally at said location rotating about a generally vertical axis and upwardly through which mass the combustion gases passing upwardly from the lower region of the furnace must pass, subjecting the unburned liquor portions as well as the non-combustibles moving upward through the furnace with the combustion gases to this whirling mass so that at least a portion of the unburned liquor will be intimate relation with this additional air mass and will be burned and so that a whirling motion will be imparted to this material in these gases causing at least a part thereof to be thrown outwardly into the chemicals descending along the furnace walls and carried downward therewith.

3. The method of burning the combustibles in the residual liquor obtained in the chemical digestion process of cellulose bearing material and smelting the chemicals in the liquor and recovering the smelted chemicals, wherein the liquor is burned in a furnace in a manner such that the walls of thefurnace are covered with downwardly flowing molten .chemical for a predetermined distance above the bottom of the furnace and the molten chemicals are collected in the bottom of the furnace and the combustion gases are passed upwardly through and out of the furnace, the improvement comprising thev steps of spraying the liquor into the furnace at a given location intermediate the bottom of the furnace and thev of liquor solids collected on the bottom, drying a major` portion ofthe liquor, burning the combustibles and smelting the chemicals in said major portion in the furnace below said given location with minor amounts of solids being entrained in the upwardly moving gas stream thatv is formed, introducing additional air for supporting combustion into the furnace above said given location but below the upper` limit of the covering of molten chemical on the furnace walls and in streams projected from a' plurality of laterally spaced locations disposed generally in a commony horizontal plane with the streams being directed tangent to an imaginary Vertical cylindei generally centrally of the furnace and forming a whirling gas mass rotating abouta generally vertical axis, subjecting the gases rising upwardly through the furnace together with-` the material entrained therein to this whirling gas mass, burning a portion of the combustibles in said material upon contact with this mass, imparting a whirling motion to the material upon being subjected to this whirling mass of gas and depositing through the centrifugal force thus developed a portion thereof into the molten chemicals flowing down the furnace Walls, and removing smelted chemicals from the lower end of the furnace.

4. The method of burning residual liquor in a furnace, and recovering chemicals therefrom, said liquor being obtained in the chemical digestion process of cellulose bearing material, and utilizing a portion of the heat evolved comprising introducing a spray of said liquor into said furnace in an upwardly rising column of hot combustion gases, maintaining said liquor spray in suspension in said rising column a sufficient time to evaporate most of the moisture therefrom, passing a major portion of said liquor down through said column of rising combustion gases and collecting portions thereof in a pile at the bottom of said furnace, introducing primary air for combustion, adjacent to said pile and directed generally toward said pile, burning a major portion of said liquor in said pile and in suspension while the liquor is descending to said pile and smelting chemical in the liquor, entraining minor amounts of the liquor in said rising gas stream, forming a downwardly flowing layer of molten chemical on the walls of the furnace about said rising gas stream from an elevation substantially above the location of introduction of the liquor into said gas stream, introducing additional combustion supporting air into said rising column of gases at a location above the introduction of the spray thereinto but below the upper end of said downwardly flowing layer o-f molten chemical and in streams that are directed generally tangent to an imaginary vertical cylinder located within the walls of said furnace and in a manner to create a whirling gas mass rotating about a generally vertical axis, passing the rising combustion gases and material entrained therein up through said whirling mass thereby intimately contacting said entrained material with said additional air, burning a portion of the combustibles in said material upon contact with said mass, imparting a whirling motion to said material upon contacting said whirling mass and depositing through the centrifugal force thus developed a portion thereof into the molten chemicals owing down the furnace walls, and passing the combustion gasesk generated from the burning liquor over heat exchanger surface after traversal of said whirling mass, recovering chemicals from the resulting smelt.

5. The method of burning the combustibles in the residual liquor obtained in the chemical digestion process of cellulose bearing material and smelting the chemicals in the liquor and recovering the smelted chemicals, wherein theliquor is burned in a furnace in a manner such that the walls of the furnace are covered with downwardly flowing molten chemical for a predetermined distance above the bottom of the furnace andthe molten chemicals are collected in the bottom of the furnace and the combustion gases are passed upwardly through and out of the furnace, the improvement comprising the steps of spraying the liquor into the furnace at a given location intermediate the bottom of the furnace and the upper limit of the downwardly owing covering. of molten chemical on the furnace walls, introducing primary airv for supporting combustion into the furnace adjacent the bottom thereof and directed generally, toward a pile of liquor solids collected on the bottom, drying a major. portion of. the liquor, burning the combustibles and smelting the .chemicals in said major portionintthe furnace` below said given location with minor amounts of solids being entrainedV in the upwardlyv moving gas stream thatv is formed, introducing additional airfor supporting combustion into the furnace and above said given location but below the upper limit of the covering of molten chemical on the furnace walls, said additional air being.

8. introduced throughthe furnace walls in streams that are spaced about the periphery ofthe furnace' andare di-A rected in such a manner as. to create va whirling mass of gas generally at said location rotating about a generally` vertical. axis and disposed so the upwardly rising gases therebelow must pass therethrough. and the solids entrained therein willintimately contact said mass of` gas, subjecting the gases rising upwardly. through the furnace together with thematerial entraine'd therein to thiswhirl# ing gas mass, burning a portion of the combustibles in said material upon contact with this mass, imparting a whirling motion to the material upon .being subjectedrto this whirling massV of gas and depositing through the cem trifugal force thus developed a portion thereof into'the molten chemicals owing. down the furnace walls, and removing. smelted chemicals. from the lower endl. of the furnace.

References Citedfin the lel ofthis patent UNITED STATES PATENTS 2,262,420 Badenhausen .7 .Y- Nov. 11,v 1941 2,535,730 Gadret Dec. 26, 1950 2,582,792 Paren' 1.. Jan.v 15,1952 2,590,905 Tomlinson et ali. ...M Apr. 1, 1952y 2,591,188 Nilsson Apr. 1, 1952y 2,636,813 Singleton Apr. 28, 17.953 2,739,878 Jolley f Mar. 27, 1956 FOREIGN PATENTS" 658,471 Great Britain -..7---- Oct. 10,1951 

1. IN A VERTICALLY DISPOSED CHEMICAL RECOVERY FURNACE WITHIN WHICH THE COMBUSTIBLES IN THE RESIDUAL LIQUOR OBTAINED IN THE CHEMICAL DIGESTION PROCESS OF CELLULOSE BEARING MATERIAL IN THE MANUFACTURE OF PAPER IS BURNED, WITH THE WALLS OF THE FURNACE BEING COVERED WITH DOWNWARDLY FLOWING MOLTEN CHEMICAL FOR A PREDETERMINED DISTANCE ABOVE THE BOTTOM OF THE FURNACE AND WITH THE CHEMICALS IN THE LIQUOR BEING COLLECTED IS THE BOTTOM OF THE FURNACE AND THE COMBUSTION GASES PASSONG UPWARDLY THROUGH AND OUT OF THE FURNACE, THE IMPROVEMENT COMPRISING THE STEPS OF SPRAYING THE LIQUOR INTO THE FURNACE AT A GIVEN LOCATION INTERMEDIATE THE BOTTOM OF THE FURNACE AND THE UPPER LIMIT OF THE COATING OF MOLTEN CHEMICAL ON THE FURNACE WALLS WITH MOST OF THE LIQUOR REMAINING FREE OF CONTACT OF THE FURNACE WALLS AND DESCENDING TOWARD THE FURNACE BOTTOM, INTRODUCING THE PRIMARY AIR FOR SUPPORTING COMBUSTION INTO THE FURNACE ADJACENT THE BOTTOM THEREOF AND IN A DIRECTION GENERALLY UPON LIQUOR SOLIDS COLLECTED ON THE BOTTOM, DRYING A MAJOR PORTION OF THE LIQUOR, BURNING THE COMBUSTIBLES AND SMELTING THE CHEMICALS IN SAID MAJOR PORTION IN THE FURNACE BELOW SAID GIVEN LOCATION WITH MINOR AMOUNTS OF SOLIDS BEING ENTRAINED IN THE UPWARDLY MOVING GAS STREAM, INTRODUCING ADDITIONAL AIR FOR SUPPORTION COMBUSTION INTO THE FURNACE ABOVE SAID GIVEN LOCATION BUT BELOW THE UPPER LIMIT OF THE COATING OF MOLTEN CHEMICAL ON THE FURNACE WALLS, SAID ADDITIONAL AIR BEING INTRODUCED THROUGH THE FURNACE WALLS IN STREAM THAT ARE SPACED ABOUT THE PRIPHERY OF THE FURNACE AND ARE DIRECTED IN SUCH A MANNER AS TO CREATE A WHIRLING MASS OF GAS GENERALLY AT SAID LOCATION ROTATING ABOUT A GENERALLY VERTICAL AXIS AND DISPOSED SO THE UPWARDLY RISING GASES THEREBELOW MUST PASS THERETHROUGH AND THE SOLIDS ENTRAINED THEREIN WILL INTIMATELY CONTACT SAID MASS OF GAS, SUBJECTING THE GASES RISING UPWARDLY THROUGH THE FURNACE TOGETHER WITH THE MATERIAL ENTRAINED THEREIN TO THIS WHIR ING GAS MASS, BURNING A PORTION OF THE COMBUSTIBLES IN SAID MATERIAL UPON CONTACT WITH THIS MASS, IMPARTING A WHIRLING MOTION TO THE MATERIAL UPON BEING SUBJECTED TO THIS WHIRLING MASS OF GAS AND DEPOSITING THROUGH THE ENTRIFUGAL FORCE THUS DEVELOPED A PORTION THEREOF INTO THE MOLTEN CHEMICALS FLOWING DOWN THE FURNACE WALLS AND REMOVING SMELTED CHEMICALS FROM THE LOWER END OF THE FURNACE. 